Conventionally, substrates formed with a tin-oxide-containing indium oxide (hereinafter referred to as “ITO”) film have been used as liquid crystal display elements for use in color liquid crystal panels and the like.
With a general ITO film-formed substrate, a structure is adopted in which a color filter, an organic protective film, and an ITO film are formed in this order from the bottom upwards on a surface of a glass substrate.
The ITO film formed on the substrate surface functions as an electrode of the substrate, and the electrode pattern is usually formed using a photolithography method. In the photolithography method, it is necessary to pattern the electrode pattern into the ITO film on the substrate using a strong acid, and then strip off a resist used in the patterning using a strong alkali; chemical resistance and adhesion are thus required of the substrate, so that peeling off of the ITO film from the substrate due to the strong acid and/or the strong alkali used in these two steps can be prevented. Consequently, from hitherto, to improve the adhesion between the ITO film and the organic protective film, an SiO2 film has been deposited through a high-frequency sputtering method as an intermediate layer between the ITO film and the organic protective film.
Furthermore, a substrate that uses a conventional intermediate layer comprised of an SiO2 film has a problem that the chemical resistance, in particular the alkali resistance, is low, and hence as a film deposition method for resolving this problem, a method has been disclosed in which a metal nitride film of SiNx or the like is interposed between the ITO film and the organic protective film, and moreover a metal oxide film of SiOx or the like is interposed between the metal nitride film and the ITO film (Japanese Laid-Open Patent Publication (Kokai) No. 6-148618).
However, although the method disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 6-148618 is certainly capable of improving the alkali resistance of the substrate, it is a valid method only for forming an SiOx film as an intermediate layer through a reactive sputtering method using Si as a target and O2 as an introduced gas, and is not a valid method for forming an SiO2 film through a high-frequency sputtering method as used as an intermediate layer from hitherto. In this way, with this conventional method, a high-frequency sputtering method, which is generally capable of forming a film having higher adhesion than with a reactive sputtering method, cannot be used. There has thus been a problem that the adhesion is worse than with an SiO2 film conventionally used as an intermediate layer.
Moreover, regarding the alkali resistance of a substrate obtained through this conventional film deposition method, the above required properties are not sufficiently satisfied.
It is an object of the present invention to provide an ITO film-formed substrate having excellent alkali resistance and adhesion, and a manufacturing method thereof.